armature disappears when importing a skinned character in obj, format?
Obj format that supports only geometry and does not support rigs or animations. 


  The OBJ file format is a simple data-format that represents 3D geometry alone — namely, the position of each vertex, the UV position of each texture coordinate vertex, vertex normals, and the faces that make each polygon defined as a list of vertices, and texture vertices. -wikipedia


For animations you should use some other format. Fbx for example is supported by most 3d software and popular game engines Unity and Unreal.